The present invention relates to a copier, printer, facsimile apparatus or similar image forming apparatus and more particularly to an image forming apparatus including a developing device using a developing liquid and an intermediate transfer body.
An image forming apparatus of the type including a developing device using a developing liquid is conventional. The developing liquid is a mixture of toner particles and a carrier liquid. The developing device develops an electrostatic latent image formed on an image carrier with the developing liquid to thereby produce a corresponding toner image. The toner image is transferred from the image carrier to a paper or similar recording medium. To deposit the toner particles on the image carrier at the time of development and to transfer them from the image carrier to the paper at the time of image transfer, the above apparatus uses the electophoresis of the toner particles charged by the carrier liquid.
An image forming apparatus of the type using an intermediate transfer body is also conventional. This type of image forming apparatus transfers toner images sequentially formed on an image carrier to the intermediate transfer body one above the other (primary transfer) and then transfers the resulting composite toner image to a paper (secondary transfer). The intermediate transfer body has customarily been used in a color image forming apparatus, which forms a color image on a paper.
The following problem arises when the intermediate transfer body is applied to the color image forming apparatus including the developing device using the developing liquid. When toner images of different colors (e.g. four colors) are transferred from the image carrier to the intermediate transfer body one above the other, the secondary transfer ratio from the transfer body to a paper decreases.
We conducted a series of researches and experiments for solving the above problem and found the following. Every time a toner image of one color is transferred from the image carrier to the intermediate transfer body, the solid matter content of the developer deposited on the transfer body increases. As a result, the apparent amount of charge of the dense group of toner particles becomes smaller than the sum of the charges, which the toner particles individually had. Consequently, the charge to contribute to the electrophoresis for the secondary transfer decreases and obstructs the transfer of the toner particles to a paper.
The image forming apparatus with the above developing device and intermediate transfer body generally includes a cleaning device for cleaning the transfer body with a cleaning blade or similar cleaning member. The problem with the cleaning member is that when it is formed of rubber belonging to a family of elastic materials, the blade lacks in durability and cannot implement the expected cleaning ability.
Further, the carrier liquid on the intermediate transfer body would render image transfer insufficient if too small in amount or would cause the image to flow if too great in amount. Particularly, when four toner images of different colors are sequentially transferred from the image carrier to the intermediate transfer body, the amount of the carrier liquid on the transfer body tends to sequentially increase from the second color to the fourth color. It is therefore necessary to accurately control the amount of the carrier liquid on the intermediate transfer body.